While there is no specific saint commemorated on this day in the General Roman Calendar, December 18th is significant for the ongoing recitation of the 'O Antiphons' during Vespers, which are ancient prayers proclaiming various titles of the Messiah.
The 'O Antiphons' provide a rich theological reflection on the Person of Christ, using titles like 'O Adonai' (Lord) and 'O Radix Jesse' (Root of Jesse). They invite us to deepen our understanding and anticipation of the Incarnation.
O Adonai, sacred Leader of the House of Israel, who appeared to Moses in the flame of the burning bush and gave him the law on Sinai: Come and with outstretched arm redeem us.